Illumination systems comprising a plurality of luminaires, which utilize transmitting data from the individual luminaires in the light emitted are known. WO2006/079199 discloses a lighting device containing light emitting diodes, LEDs, which are driven e.g. by a pulse width modulation signal, PWM, onto which signal a data signal is modulated. Further, a sensing means is utilized to receive the data signal in the light emitted by the LEDs through detecting all (or part) of the illumination provided by the LEDs. The data signal is subsequently extracted from the detected illumination.
This kind of technique has more recently been used in point-and-control methods for luminaires. Typically, a handheld selection device is arranged to select and control individual luminaires by pointing at one or more luminaire and identifying the luminaire by means of its retrieved identification code. The identification code may be contained in the luminaire and transmitted to the selection device by modulating the light output from the luminaire in an invisible way, e.g. by means of pulse width modulation, PWM. The identification code is thus modulated onto the average light intensity outputted from the luminaire. This enables the selection device to select a luminaire based on the retrieved identification code in its directional field of view.
However, the above described systems—where the data, e.g. in the form of identification codes, is emitted in and detected from the emitted light—have several problems. When receiving identification codes from a plurality of luminaires, the receiver may not be able to resolve the individual signals for several reasons, e.g. due to low light intensities, obstructing objects in the room, distortion of the modulation signal, etc.